Modulation of GCN2/eIF2α/ATF4 Pathway in the Liver and Induction of FGF21 in Young Goats Fed a Protein- and/or Phosphorus-Reduced Diet

Abstract

Mammals respond to amino acid (AA) deficiency by initiating an AA response pathway (AAR) that involves the activation of general control nonderepressible 2 (GCN2), phosphorylation of eukaryotic translation initiation factor 2α (eIF2α), and activation of transcription factor 4 (ATF4). In this study, the effects of protein (N) and/or phosphorus (P) restriction on the GCN2/eIF2α/ATF4 pathway in the liver and the induction of fibroblast growth factor 21 (FGF21) in young goats were investigated. An N-reduced diet resulted in a decrease in circulating essential AA (EAA) and an increase in non-essential AA (NEAA), as well as an increase in hepatic mRNA expression of GCN2 and ATF4 and protein expression of GCN2. Dietary N restriction robustly increased both hepatic FGF21 mRNA expression and circulating FGF21 levels. Accordingly, numerous significant correlations demonstrated the effects of the AA profile on the AAR pathway and confirmed an association. Furthermore, activation of the AAR pathway depended on the sufficient availability of P. When dietary P was restricted, the GCN2/eIF2α/ATF4 pathway was not initiated, and no increase in FGF21 was observed. These results illustrate how the AAR pathway responds to N- and/or P-reduced diets in ruminants, thus demonstrating the complexity of dietary component changes.

Effects of dietary nitrogen and/or phosphorus reduction on mineral homeostasis and regulatory mechanisms in young goats

“…The clinical health of the animals was ensured through monitoring and care by a qualified veterinarian that examined the animals daily and closely monitored their behavior and physical condition. The data on feed intake, daily weight gain and BW of the goats have been previously published (23). The data on feed intake are listed in Table 3.…”

“…For this molecular study, organs and blood samples were obtained from animals of a previous study (23) to avoid unnecessary repetition of animal model experiments. In brief, 28 male colored German goats from a commercial goat farm were selected for this experiment.…”

“…Individual feeding took place daily at 08.00 and 16.00 for 6 to 8 weeks. At the start of the experiment, the animals were 10 weeks old with an initial body weight (BW) of 19.04 kg (SEM 0.08) (23). A feed manufacturer specializing in feed production for animal research (ssniff Spezialdiäten GmbH, Soest, Germany) manufactured the pellets for the diets.…”

“…All diets were isoenergetic, and contained approximately 12.7 MJ ME/kg DM. For further details on ingredients and chemical composition of the diets, see Weber et al (23). Each feeding group consisted of seven animals housed together and received water ad libitum.…”

“…Cytosolic preparation was required for quantification of ERK1/2, whereas crude membranes (CM) were isolated for quantification of Na + /K + -ATPase, both in accordance with the method of Wilkens et al (36). Total cell lysate preparation was required to determine CYP27B1 and FGFR1 protein expression in accordance with the method of Weber et al (23). Protein concentrations of all cell fractions were measured using a commercial Bradford assay .…”